The present invention relates to an oil level sensor for detecting the level of lubricating oil in an internal combustion engine.
In an industrial engine, if the engine is operated without noticing a shortage of the lubricating oil, the engine becomes damaged due to burning.
Consequently, an oil level sensor is provided for monitoring the level of the lubricating oil at all times. When the oil sensor detects a lower level for the oil lower than a set level, the engine is stopped or an alarm lamp is turned on to prevent the engine from being damaged.
Japanese Patent Applications Laid-Open 62-93417 and 62-26379 disclose oil sensors employed with an oil pressure switch and a reed switch, respectively.
The oil sensor employed with the reed switch consists of various components such as a float and a magnet in addition to the reed switch, so that the oil sensor is complicated in construction. Further, the sensor must be assembled in a crankcase before assembling the engine.
The oil sensor employed with the oil pressure switch can not be used for an engine without an oil pump.
To the contrary, a fluid sensor detects the amount of fluid by measuring a resistance of the fluid.
The fluid sensor comprises a center electrode and an outer electrode surrounding the center electrode at a predetermined distance. The fluid sensor detects the volume and concentration of the fluid, and other conditions in accordance with the variation of the resistance between the center electrode and the outer electrode.
The variation of the resistance is detected by measuring a current flowing in the fluid sensor. However, the current representing the variation of the resistance of oil is very small, because the resistance is large. Thus, a shielded wire must be employed for a signal line in order to prevent the influence of noises. However, it is difficult to completely eliminate the influence of noise.
Further, the shielded wire must be connected to a control unit by a connector, which causes an increase of parts and the assembling process.
Moreover, a high-insulating resistor must be provided in the control unit. However, the high-insulating resistor electrically affects other circuits.